The philosophy of science is the branch of philosophy which deals with the study of science (in the sense of "natural science"). The philosophy of science is closely related to epistemology. It seeks to explain such things as the nature of scientific statements, the way in which they are produced, how it is that they provide us with such power over our environment and the implications of science for the larger society, and for the sciences themselves.

This article is not exhaustive; it covers only those topics that are seen as central by all of the major philosophies of science. As with the philosophy of mathematics, there tend to be 'schools' of scientific thought, each of which adheres to its own principles. 'Each of these in future deserves its own article(s)'.

Scientific Statements

The answer to this question might appear obvious, but philosophers like to push obvious answers to their limits.

Empiricism

In some way, scientific statements link to and are subject to our experiences or observations. Empiricism is the doctrine that knowledge derives from experience of the world, in contrast to idealism, which holds that knowledge derives from ideas.

Experiments are observations that have been especially set up to test a theory. They are used to gather information through our senses, via empirical methods that many humans are capable of experiencing. Once reproduced widely enough by many scientists, this information counts as evidence, upon which the scientific community bases its explanations of how things work.

Observations involve philosophy of perception, and so are themselves cognitive acts. That is, observations are themselves embedded in our understanding of the way in which the world works, and as this understanding changes, the observations may apparently change.

Realism

Realism or naive empiricism in the context of the philosophy of science is the belief that scientific statements are in some way about a world that exists independently of our ideas and theories about it. Realists hold that things like electrons and magnetic fields actually exist. It is na?ve in the sense of being straightforward, not in any pejorative sense, and is the view that most scientists would themselves adopt. For realists, empirical method is used to test theories against the real world.

Instrumentalism

Instrumentalism, deriving from John Dewey's pragmatism, holds in contrast to realism that what is important is the predictive power of scientific statements. To an instrumentalist, electrons and magnetic fields are convenient ideas that do not necessarily correspond to some 'real world' but which are important because they permit us to control and predict events in our environment. Instrumentalism is similar in many regards to phenomenalism. For instrumentalists, empirical method is used to do no more than show that theories are consistent with observations.

Social Constructivism

Some historians, philosophers, and sociologists of science believe that scientific theories are shaped by their social and political context. This approach is usually known as social constructivism. Social constructivism is in one sense an extension of instrumentalism that incorporates the social aspects of science. In its strongest form, it sees science as merely a discourse between scientists, with objective fact playing a small role if any. A weaker form of the constructivist position might hold that social factors play a large role in the acceptance of new scientific theories.

On the stronger account, the existence of Mars the planet is irrelevant, since all we really have are the observations, theories and myths, which are all themselves constructed by social interaction. On this account, scientific statements are about each other, and an empirical test is no more than checking the consistency between different sets of social constructed theories. It becomes difficult, then, to explain how science differs from any other discipline. But equally, it becomes difficult to give an account of the extraordinary success of science in producing useable technology.

On the weaker account, Mars the planet might be said to have a real existence, separate and distinct from our observations, theories and myths about it. Although theories and observations are socially constructed, part of the construction process involves ensuring a correspondence of some sort with this reality. On this account, scientific statements 'are' about the real world. The crucial issue for this account is justifying this correspondence. It is important, therefore, to consider how scientific statements are justified.

Reductionism

Reductionism in science can have several different senses. Reductionism is distinct from analysis, the activity of breaking an observation or theory down into simpler concepts in order to understand it. Analysis is as essential to science as it is to all rational enterprises.

One type of reductionism is the belief that all fields of study are ultimately amenable to scientific explanation. Perhaps an historical event might be explained in sociological and psychological terms, which in turn might be reduced to physiology and ultimately to chemistry and physics. This might be seen as implying that the historical event was 'nothing but' the physical event, denying the existence of emergent phenomena.

Such objections to reductionism are what Daniel Dennett calls greedy reductionism, which he claims is just 'bad science', seeking to find explanations which are appealing or eloquent, rather than those that are of use in predicting natural phenomena.

Scientific Justification

The most powerful statements in science are those with the widest applicability. Newtons Second Law - for every action there is an opposite and equal reaction is a powerful statement because it applies to every action, anywhere, and at any time.

But it is not possible for scientists to have tested every incidence of an action, and found a reaction. How is it, then, that they can assert that the Second Law is in some sense true? They have, of course, tested many, many actions, and in each one have been able to find the corresponding reaction. But can we be sure that the next time we test the Second Law, it will be found to hold true?

Induction

One solution to this problem is to rely on the notion of induction. Inductive reasoning maintains that if a situation holds in all observed cases, then that the situation holds in all such cases. So, after completing a series of experiments that support the Second Law, one is justified in maintaining that the Law holds in all cases.

Explaining why induction is true has been somewhat problematic. One cant use deduction, the usual process of moving logically from premise to conclusion, because there is simply no syllogism that will allow such a move. No matter how many time 17th Century biologists observed white swans, and in how many different locations, there is no deductive path that can lead them to the conclusion that all swans are white. This is just as well, since, as it turned out, that conclusion would have been wrong. Similarly, it is at least possible that an observation will be done tomorrow that shows an occasion in which an action is not accompanied by a reaction; the same is true of any scientific law.

One answer has been to conceive of a different form of rational argument, one that does not relying on deduction. Whereas deduction allows one to formulate a specific truth from a general truth (all crows are black; this is crow; therefore this is black), induction somehow allows one to formulate a general truth from some series of specific observations (this is a crow and it is black; that is a crow and it is black; therefore all crows are black).

The problem of induction is one of considerable debate and moment in the philosophy of science: is induction indeed justified, and if so, how?

Falsifiability

Another way to use logic to justify scientific statements, first formally discussed by Karl Popper is falsifiability. Falsifications aim is to re-introduce deductive reasoning into the debate. It is not possible to deduce a general statement from a series of specific ones, but it is possible for one specific statement to prove that a general statement is false. Finding a black Swan might be sufficient to show that the general statement 'all swans are white' is false.

Falsifiability neatly avoids the problem of induction, because it does not make use of inductive reasoning. However, it introduces its own difficulties. When an apparent falsification occurs, it is always possible to introduce an addition to a theory that will render it unfalsified. So, for instance, ornithologists might have simply argued that the large black bird found in Australia was not a member of the genus Cygnus, but of some other, or perhaps some new, genus.

Coherentism

Induction and Falsification both attempt to justify scientific statements by reference to other specific scientific statements. Both must avoid the problem of the criterion, in which any justification must in turn be justified, resulting in an infinite regress. The regress argument has been used to justify one way out of the infinite regress, foundationalism. Foundationalism claims that there are some basic statements that do not require justification. Both induction and falsification are forms of foundationalism in that they rely on basic statements that derive directly from observations.

The way in which basic statements are derived from observation complicates the problem. Observation is a cognitive act; that is it relies on our existing understanding  our set of beliefs. An observation of a transit of Venus requires a huge range of auxiliary beliefs, such as those that describe the optics of telescopes, the mechanics of the telescope mount, and an understanding of celestial mechanics. Prima facie, the observation does not appear to be basic.

Coherentism offers an alternative by claiming that statements can be justified by their being a part of a coherent system. In the case of science, the system is usually taken to be the complete set of beliefs of an individual or of the community of scientists. W. V. Quine argued for a Coherentist approach to science. An observation of a transit of Venus is justified by its being coherent with our beliefs about optics, telescope mounts and celestial mechanics. Where this observation is at odds with one of these auxiliary beliefs, an adjustment in the system will be required to remove the contradiction.

Occam's Razor

Occam's Razor is another notable touchstone in the philosophy of science. William of Ockham (or Ockhegm or several other spellings) suggested that the simplest account which 'explains' the phenomenon is to be preferred. He did not suggest that it would be true, or even more likely to be true, though 'simpler' has very often turned out to be more likely to be right (in hindsight) than 'more complex'.

Occam's Razor has usually been used just as a rule of thumb for choosing between equally 'explanatory' hypotheses (ie, theories) about one or more observed phenomena. However, it is rare that two theories explain equally, so its use has been limited. There are now mathematical approaches based on information theory that balance explanatory power with simplicity. One such is minimum message length inference.

Occam's Razor is often abused and cited where it is inapplicable. It does not say that the simplest account is to be preferred regardless of its capacity to explain outliers, exceptions, or other phenomena in question. The principle of falsifiability requires that any exception that can be reliably reproduced should invalidate the simplest theory, and that the next-simplest account which can actually incorporate the exception as part of the theory should then be preferred to the first.

Social Accountability

Scientific Infallibility

A critical theme in science is to what degree the current body of scientific knowledge can be taken as an indicator of what is actually 'true' about the physical world in which we live. The acceptance of knowledge as if it were absolutely 'true' and unquestionable (in the sense of theology or ideology) is rejected by scientists.

However, it is common for members of the public to have the opposite view of science; many lay people believe that scientists are making claims of infallibility. Many in the scientific community are concerned about the wide disparity between how scientists work, and how their work is perceived. Many scientists are thus involved in public education campaigns to educate lay people in high schools and colleges about scientific skepticism and the scientific method.

Critiques of Science

Paul Feyerabend argued that no description of scientific method could possibly be broad enough to encompass all the approaches and methods used by scientists. Feyerabend objected to prescriptive scientific method on the grounds that any such method would stifle and cramp scientific progress. Feyerabend claimed 'the only principle that does not inhibit progress is: anything goes'.